Hard chrome plating (electrodeposited functional chromium, AMS 2406) Hard chrome

spore: profile
id: hard-chrome-plating
spore_version: 0.2
family: coatings
name: Hard chrome plating (electrodeposited functional chromium, AMS 2406)
abbreviation: Hard chrome
role: wear and friction coating on steel
category: coatings
type: anodize
summary: |
  Hard chromium is an electroplated layer of chromium metal that is built up on steel parts to resist wear and reduce friction. Armoloy gives a hardness of HRC 65-68 for the plate, and the Wikipedia article gives 65 to 69 HRC. Armoloy also gives a commonly used thickness of 25 µm to 762 µm. The plating bath uses chromium trioxide with sulfuric acid, and the Lobachemie safety data sheet for chromium trioxide carries the cancer hazard statement H350.
best_for: Wear-resistant, low-friction steel parts that need a thick, hard chromium layer, such as worn parts rebuilt to size (NASA Class 2 plating)
weakest_at: The chromium trioxide bath is hazardous, and the plate often has cracks, so NASA's specification calls for shot peening before plating when it is specified
identity:
  formula: Cr (electrodeposited chromium metal, plated from a chromic acid bath of chromium trioxide and sulfuric acid)
  source: nasa-prc-5003
  where: Section 3.0 (chromium plate on steel). Bath composition from the Hard chrome article on Wikipedia, Bath chemistry section.
  designations:
    - system: AMS
      code: '2406'
      note: Electrodeposited Hard Chrome Specification
      source: armoloy-ams-2406
      where: Page title
tags:
  environments: []
  stresses: []
  applications:
    - mechanisms
properties:
  - benchmark: vickers_hardness
    label: Vickers hardness, industrial hard chromium electroplate (stated range)
    value: 940
    value_high: 1210
    bound: range
    unit: HV
    scope: material
    conditions:
      form: industrial hard chromium electroplate
      note: the page says the range depends on plating thickness, and gives no thickness
    method: Stated range on a manufacturer's page (the page names Vickers and Rockwell C as the test scales)
    status: ground
    source: uschrome
    where: Hardness section, first line ("65-70 HRc or 940-1210 HV")
  - benchmark: rockwell_c_hardness
    label: Rockwell C hardness, industrial hard chromium electroplate (stated range)
    value: 65
    value_high: 70
    bound: range
    unit: HRc
    scope: material
    conditions:
      form: industrial hard chromium electroplate
      note: the page says the range depends on plating thickness, and gives no thickness
    method: Stated range on a manufacturer's page
    status: ground
    source: uschrome
    where: Hardness section, first line ("65-70 HRc or 940-1210 HV")
  - benchmark: vickers_hardness
    label: Vickers hardness, chromium electroplated (Hard Chrome) as listed on the page
    value: 1210
    unit: HV
    scope: material
    conditions:
      form: chromium electroplated (Hard Chrome)
      note: the page lists this value beside 70 HRc
    method: Single value stated on a manufacturer's page
    status: ground
    source: uschrome
    where: Hardness section, line "Chromium electroplated (Hard Chrome)"
  - benchmark: rockwell_c_hardness
    label: Rockwell C hardness, hard chrome plate (stated range)
    value: 65
    value_high: 68
    bound: range
    unit: HRC
    scope: material
    conditions:
      form: hard chrome plate
      note: no test conditions are stated on the page
    method: Stated range on a manufacturer's page
    status: ground
    source: armoloy-hard-chrome
    where: Benefits list, "Increased Hardness" line
  - benchmark: rockwell_c_hardness
    label: Rockwell C hardness, hard chrome (stated range)
    value: 65
    value_high: 69
    bound: range
    unit: HRC
    scope: material
    conditions:
      form: hard chromium plate
      note: the article says the hardness also depends on the base metal's hardness
    method: Stated range in an encyclopaedia article
    status: ground
    source: wikipedia-hard-chrome
    where: Hardness section
  - benchmark: coefficient_of_friction
    label: Coefficient of friction of hard chrome against steel
    value: 0.12
    value_high: 0.21
    bound: range
    unit: '-'
    scope: material
    conditions:
      lubrication: unlubricated
      counterface: steel
    method: Stated range on a manufacturer's page
    status: ground
    source: armoloy-hard-chrome
    where: Coefficient of friction line ("Roughly 0.12-0.21 Against Steel (Unlubricated)")
  - benchmark: deposit_thickness
    label: Typical deposit thickness of hard chrome
    value: 25
    value_high: 762
    bound: range
    unit: µm
    scope: material
    conditions:
      basis: typical range on the page (the page says commonly), not a limit
    method: Stated range on a manufacturer's page
    status: ground
    source: armoloy-hard-chrome
    where: Deposit thickness line ("Commonly 0.001 to 0.030 inches (25 µm to 762 µm)")
  - benchmark: deposit_thickness
    label: Final thickness after grinding, NASA Class 2 engineering chromium plate
    value: 0.002
    value_high: 0.005
    bound: range
    unit: inch
    scope: material
    conditions:
      class: Class 2 engineering plating
      state: final thickness after grinding
      example: example drawing note in Section 3.0
    method: Specification requirement for the drawing note
    status: ground
    source: nasa-prc-5003
    where: Section 3.0 Usage, second example drawing note ("0.0020-0.0050 INCHES")
  - benchmark: deposit_thickness
    label: Thickness, NASA Class 1 corrosion-protective chromium plate, Type II
    value: 0.0005
    value_high: 0.0015
    bound: range
    unit: inch
    scope: material
    conditions:
      class: Class 1 corrosion-protective plating, Type II satin finish
      example: example drawing note in Section 3.0
    method: Specification requirement for the drawing note
    status: ground
    source: nasa-prc-5003
    where: Section 3.0 Usage, first example drawing note ("0.0005-0.0015 INCHES")
  - benchmark: bath_temperature
    label: Hard chrome bath operating temperature
    value: 50
    value_high: 65
    bound: range
    unit: °C
    scope: material
    conditions:
      bath: hexavalent chromium bath (chromium trioxide and sulfuric acid)
      note: the article says higher current density needs a higher bath temperature
    method: Stated range in an encyclopaedia article
    status: ground
    source: wikipedia-hard-chrome
    where: Bath chemistry section (printed as "50 to 65 °C (120 to 150 °F)")
  - benchmark: bath_ph
    label: Hard chrome bath pH
    value: 0
    unit: '-'
    scope: material
    conditions:
      bath: hexavalent chromium bath (chromium trioxide and sulfuric acid)
    method: Stated value in an encyclopaedia article
    status: ground
    source: wikipedia-hard-chrome
    where: Bath chemistry section ("pH 0")
  - benchmark: density
    label: Density of pure chromium metal (element), not measured on the electrodeposit
    value: 7.192
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 °C
      form: pure chromium element
    method: Value printed in the element's properties table
    status: ground
    source: wikipedia-chromium
    where: Physical properties (infobox), "7.192 g/cm3 (at 20° C)"
  - benchmark: melting_point
    label: Melting point of pure chromium metal (element), not measured on the electrodeposit
    value: 1907
    unit: °C
    scope: material
    conditions:
      form: pure chromium element
    method: Value printed in the element's properties table
    status: ground
    source: wikipedia-chromium
    where: Physical properties (infobox), printed as "2180 K (1907 °C, 3465 °F)"
corrosion:
  - environment: Steel parts in rural, industrial or marine air (NASA Class 1 corrosion-protective plating)
    headline: NASA's specification says the chromium plate protects steel against corrosion, but the plate often has cracks that run down to the steel.
    effect: The specification says Class 1 plate protects steels against corrosive attack in rural, industrial or marine environments, and that the protection depends on deposit thickness. It also says chromium plate often has cracks that run from the surface through the thickness to the substrate, and that shot peening before plating adds compressive stress that stops cracks from reaching the substrate.
    rating: moderate
    conditions:
      plate: Class 1 corrosion-protective chromium plate on steel
      cracks: crack frequency rises with pre-grinding plate thickness
    source: nasa-prc-5003
    where: Section 3.1 (Shot peening) and Section 3.0 (Class 1 description)
risks:
  hazards:
    - text: The chromium trioxide bath chemical (CAS 1333-82-0) is classed as Oxidising Solids Category 1 (H271), Acute toxicity inhalation Category 2 (H330) and Carcinogenicity Category 1A (H350). The SDS prints the hazard statements H271, H301+H311, H314, H317, H330, H334, H340, H350, H361f, H372 and H410 with the signal word Danger. The SDS describes the bath chemical, not the chromium deposit.
      ghs:
        - H271
        - H301+H311
        - H314
        - H317
        - H330
        - H334
        - H340
        - H350
        - H361f
        - H372
        - H410
      source: lobachemie-cr2o3-sds
      where: Section 2 (hazard identification and CLP hazard statements); Section 16 classification list
    - text: The Federal Register rule for chromium electroplating and anodizing tanks calls hexavalent chromium "a known human carcinogen".
      ghs: []
      source: fr-2012-chromium-neshap
      where: Summary of the Major Provisions, Section I.A.2
    - text: Hexavalent chromium is the most toxic form of chromium, and the plating bath releases a toxic mist that is controlled with wet scrubbers. Waste includes lead chromates from lead anodes.
      ghs: []
      source: wikipedia-hard-chrome
      where: Hexavalent chromium health concerns section
  failure_risks:
    - mode: Hydrogen-related requirement for high-strength and hardened steel after plating
      trigger: Plating high-strength or hardened steel listed in Table 1 of NASA PRC-5003
      consequence: The specification requires a hydrogen bakeout within the time limit set in Section 3.2 after plating for these steels. Armoloy's AMS 2406 page says its hydrogen embrittlement test "Ensures the plating process doesn't weaken the component." The NASA text does not describe the failure in detail.
      severity: high
      source: nasa-prc-5003
      where: Section 3.2 and Table 1 (Steels That Require a Hydrogen Bakeout after Chromium Plate)
    - mode: Cracking of the plate
      trigger: Plate built up thick before grinding
      consequence: Chromium plate often has cracks that run from the surface through the thickness to the substrate. Their frequency increases with the pre-grinding plate thickness.
      severity: moderate
      source: nasa-prc-5003
      where: Section 3.1 (Shot peening)
  side_effects:
    - text: The chromium trioxide bath gives off a toxic mist, which the article says is controlled with wet scrubbers. Exposure to the mist affects the workers and the air around the bath.
      affects: Workers and the air around the plating bath
      source: wikipedia-hard-chrome
      where: Hexavalent chromium health concerns section
  handling:
    - text: Pits and scratches on the part before plating are amplified after plating, so removing them first is recommended.
      source: nasa-prc-5003
      where: Section 2 and pre-plating preparation text, before Section 3.1
    - text: The safety data sheet for chromium trioxide calls for closed storage, and says the chemical is toxic if inhaled and carcinogenic. Handle the bath only with the controls in the supplier's safety data sheet.
      source: lobachemie-cr2o3-sds
      where: Section 7 (handling and storage) and Section 2
  mitigations:
    - text: Shot peen the part before plating, using ceramic bead as the specification sets out, to put compressive stress into the surface and stop cracks from reaching the steel.
      source: nasa-prc-5003
      where: Section 3.1
    - text: Carry out the hydrogen bakeout after plating on the steels listed in the specification's Table 1.
      source: nasa-prc-5003
      where: Section 3.2
uses:
  - application: mechanisms
    device: Worn or undersized steel machine parts rebuilt by plating
    example: NASA Class 2 plating is typically used for final dimensional thicknesses (after grinding) of 0.0020 to 0.0050 inches, and heavy deposits are used to build up worn or undersized parts.
    source: nasa-prc-5003
    where: Section 3.0 Usage (Class 2 description)
  - application: mechanisms
    device: Steel parts that need wear and abrasion resistance
    example: The Wikipedia article says hard chromium is used to reduce friction, improve wear and abrasion resistance, prevent galling or seizing, add chemical inertness, and rebuild worn parts to their original dimensions.
    source: wikipedia-hard-chrome
    where: Introduction
supply:
  - subject: Chromium
    producers:
      - country: South Africa
        share_percent: 45.1
        year: 2025
      - country: Turkey
        share_percent: 17.6
        year: 2025
      - country: Kazakhstan
        share_percent: 13.7
        year: 2025
      - country: India
        share_percent: 5.9
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (final list of 60 minerals; chromium is named as Chromium, used in stainless steel)
        listed: true
    recycling: 'USGS: in 2025, recycled chromium contained in reported stainless-steel scrap receipts accounted for 21% of apparent consumption (United States).'
    substitutes:
      - 'USGS: chromium has no substitute in stainless steel, the leading end use, or in superalloys, the major strategic end use. This statement covers chromium as an alloy addition and does not address hard chrome plating.'
    source: usgs-mcs2026-chromium
    where: 'World Mine Production and Reserves table, 2025e (shares calculated by Space Mushroom against the printed world total of 51,000 thousand t; footnote 12 says mine production is reported in gross weight); Recycling; Substitutes. Critical list: USGS 2025 critical minerals page.'
documents:
  - title: NASA/JSC PRC-5003 Rev. D, Process Specification for Electrodeposited Chromium Plating (June 2020)
    type: standard
    url: https://www.nasa.gov/wp-content/uploads/2023/03/prc-5003-current.pdf
    year: 2020
  - title: USGS Mineral Commodity Summaries 2026, Chromium
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
  - title: Lobachemie safety data sheet, Chromium trioxide (CAS 1333-82-0), revision 2025-09-15
    type: sds
    url: https://www.lobachemie.com/lab-chemical-msds/MSDS-CHROMIUM-TRIOXIDE-CASNO-1333-82-02821-EN.aspx
    year: 2025
  - title: 'Federal Register, 2012-09-19: National Emission Standards for Hazardous Air Pollutants amendments for chromium electroplating and anodizing (Subpart N)'
    type: report
    url: https://www.govinfo.gov/content/pkg/FR-2012-09-19/html/2012-20642.htm
    year: 2012
gaps:
  - No density or melting point for the electrodeposit itself was found in any source read. The density and melting point in the file are for pure chromium metal (the element), not the plate.
  - Coefficient of thermal expansion for chromium on the uschrome page is printed in exponent notation, so it is left out (verify cannot match that form).
  - No salt-spray, humidity or time-to-rust corrosion figures were found for hard chrome in any source read.
  - The uschrome chemical-resistance table does not say whether it applies to the chromium deposit, so it is not used.
  - No fatigue-strength value for hard chrome plate was found in the sources read. The NASA text says cracks can reduce fatigue, but gives no number.
  - Armoloy and uschrome say hardness depends on plating thickness, but neither gives a thickness-hardness pair.
  - AMS 2406 requirements (thickness, hardness and adhesion limits) are not printed on the Armoloy AMS 2406 page. The SAE text was not accessible in this run.
  - PubChem record for chromium trioxide returned a verification page in this run, so the Lobachemie safety data sheet was used for the hazard entry.
  - EU critical raw materials status for chromium was not checked in this run.
  - Replacement coating performance (HVOF and other thermal spray) was not quantified. The 2020 review found by search could not be opened (publisher returned 403).
  - 'Several property names are not in spores/property-canon.yaml and were used as snake_case: vickers_hardness, rockwell_c_hardness, coefficient_of_friction, deposit_thickness, bath_temperature, bath_ph.'
sources:
  uschrome:
    title: Physical and chemical properties of hard chrome
    id: web page, accessed 2026-11-02
    url: https://www.uschrome.com/physical-and-chemical-properties-of-hard-chrome
    year: 2026
    kind: web
    license: supplier web page, cited not reproduced
  armoloy-hard-chrome:
    title: Armoloy, hard chrome plating page (benefits, deposit thickness and friction)
    id: web page, accessed 2026-11-02
    url: https://armoloy.com/?p=8519
    year: 2026
    kind: web
    license: supplier web page, cited not reproduced
  armoloy-ams-2406:
    title: Armoloy, AMS 2406 Electrodeposited Hard Chrome Specification page
    id: web page, accessed 2026-11-02; supplier commentary, not the SAE text
    url: https://armoloy.com/plating-specifications/ams-2406/
    year: 2026
    kind: web
    license: supplier web page, cited not reproduced
  wikipedia-hard-chrome:
    title: Hard chrome (Wikipedia)
    id: web page, accessed 2026-11-02
    url: https://en.wikipedia.org/wiki/Hard_chrome
    year: 2026
    kind: web
    license: CC BY-SA
  wikipedia-chromium:
    title: Chromium (Wikipedia), physical properties and atomic weight
    id: web page, accessed 2026-11-02
    url: https://en.wikipedia.org/wiki/Chromium
    year: 2026
    kind: web
    license: CC BY-SA
  nasa-prc-5003:
    title: NASA/JSC PRC-5003 Rev. D, Process Specification for Electrodeposited Chromium Plating
    id: PRC-5003 Rev. D, June 2020, Engineering Directorate, Structural Engineering Division
    url: https://www.nasa.gov/wp-content/uploads/2023/03/prc-5003-current.pdf
    year: 2020
    kind: standard
    license: public domain (NASA)
  usgs-mcs2026-chromium:
    title: Mineral Commodity Summaries 2026, Chromium
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS, final list of 60 minerals)
    id: Final 2025 List of Critical Minerals, November 2025
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  lobachemie-cr2o3-sds:
    title: 'Lobachemie safety data sheet: Chromium trioxide, CAS 1333-82-0 (revision 9/15/2025, version 1.0)'
    id: CAS 1333-82-0; revision date 9/15/2025
    url: https://www.lobachemie.com/lab-chemical-msds/MSDS-CHROMIUM-TRIOXIDE-CASNO-1333-82-02821-EN.aspx
    year: 2025
    kind: datasheet
    license: supplier document, linked not reproduced
  fr-2012-chromium-neshap:
    title: 'Federal Register, 19 September 2012 (Vol. 77, No. 182): National Emission Standards for Chromium Emissions from Hard and Decorative Chromium Electroplating and Chromium Anodizing Tanks, amendments'
    id: 77 FR 58231; document 2012-20642
    url: https://www.govinfo.gov/content/pkg/FR-2012-09-19/html/2012-20642.htm
    year: 2012
    kind: report
    license: public domain (US federal government)
license: CC-BY-4.0
updated: '2026-11-02'
review:
  status: draft
  method: assistant
  checked_values: 13
  unreachable: 1
  caveats: 2
  note: Read by an AI assistant on 2026-11-02. The PubChem record and the 2020 open review of hard chrome alternatives could not be opened in this run, and the Univar SDS returned 403. Density and melting point are for the pure element.
story:
  recipe:
    line: Hard chromium is a layer of chromium metal (Cr) electroplated onto a steel part from a chromic acid bath of chromium trioxide dissolved in sulfuric acid, per the Wikipedia article's bath chemistry section.
    parts:
      - name: Chromium
        symbol: Cr
        atoms: 1
        atomic_weight: 51.996
        role: The deposited metal. The layer is built up on the steel to the thickness on the drawing, then ground back to size when required.
  risk_groups:
    - title: For people
      level: 0
      verdict: Bath is a carcinogen; deposit not checked
      lead: The plating bath uses chromium trioxide, which the supplier's safety data sheet classes with a cancer hazard statement. This profile did not read a classification for the chromium deposit itself.
      points:
        - label: The bath chemical
          line: The safety data sheet classes chromium trioxide as carcinogenic (H350), and it lists acute toxicity by inhalation (H330) and oxidising-solid hazards (H271).
        - label: The mist
          line: The Wikipedia article says the bath releases a toxic mist, which is controlled with wet scrubbers.
        - label: Regulation
          line: The US Federal Register rule for these tanks calls hexavalent chromium a known human carcinogen.
    - title: If the plate cracks or the part embrittles
      lead: These are engineering risks, not incidents. They are the reasons the NASA specification gives for its process steps.
      points:
        - label: Cracks
          line: Chromium plate often has cracks that run from the surface through the thickness to the steel. The cracks become more frequent as the plate gets thicker before grinding.
        - label: Hydrogen
          line: For high-strength and hardened steels listed in the NASA specification, a hydrogen bakeout is required after plating.
    - title: Handling and storage
      points:
        - label: Bath
          line: Store and handle chromium trioxide under the supplier's safety data sheet, which calls for closed storage and bans contact with incompatible materials.
        - label: Parts
          line: Remove pits and scratches before plating, because they are amplified by plating.
  why: Hard chromium is an electroplated layer of chromium metal that is built up on steel parts to resist wear and reduce friction. Its hardness is stated as 65 to 69 HRC by the Wikipedia article and as 65 to 68 HRC by Armoloy. The layer is applied thick enough to be ground back to size, which is why it is used to rebuild worn steel parts. The process depends on a hexavalent chromium bath, and that bath is the main safety and regulatory issue.
  uses:
    - where: Worn steel parts rebuilt to size
      line: NASA's specification says Class 2 plating is typically used for final dimensional thicknesses after grinding of 0.0020 to 0.0050 inches, and that heavy deposits build up worn or undersized parts.
    - where: Steel parts that need wear and abrasion resistance
      line: The Wikipedia article says hard chromium is used to reduce friction, improve wear and abrasion resistance, prevent galling or seizing, and rebuild worn parts to their original dimensions.
  can_do:
    - label: Strength
      line: Resist wear on steel parts, with a hardness of 65 to 69 HRC (Wikipedia) and 65 to 68 HRC (Armoloy).
    - label: Strength
      line: Run with a friction coefficient of 0.12 to 0.21 against steel without lubrication (Armoloy).
    - label: Strength
      line: Rebuild worn dimensions with a final thickness of 0.0020 to 0.0050 inches after grinding (NASA Class 2).
    - label: Strength
      line: Protect steel in rural, industrial or marine air with Class 1 plate of 0.0005 to 0.0015 inches (NASA).
  compare: Hard chromium is a thick, hard, low-friction wear layer on steel. Its hardness of 65 to 69 HRC (Wikipedia) and 65 to 68 HRC (Armoloy) is stated on supplier and encyclopaedia pages, and the NASA specification sets the plate thickness used for each class. No hardness or friction figure for the replacement coatings was read in this run, so this profile does not rank hard chrome against them. The Wikipedia article names thermal-spray coatings as replacements.
  compare_rows:
    - label: Hardness
      benchmark: rockwell_c_hardness
    - label: Friction against steel
      benchmark: coefficient_of_friction
    - label: Typical plate thickness
      benchmark: deposit_thickness
  handling:
    - The chromium trioxide bath chemical is classed as carcinogenic in its safety data sheet. Use the controls the supplier lists.
    - Remove pits and scratches before plating, because plating amplifies them.
    - Shot peen before plating when the drawing calls for it, and carry out the hydrogen bakeout on the steels that need it.
  good_for:
    - Wear on steel parts. Hardness of 65 to 69 HRC is quoted by the Wikipedia article.
    - Rebuilding worn steel parts to size. NASA's Class 2 plate is ground to 0.0020 to 0.0050 inches.
  watch_out:
    - The chromium trioxide bath. The safety data sheet classes the bath chemical as carcinogenic.
    - Cracks in the plate. NASA's specification says the plate often has cracks running to the steel.
    - Hydrogen. Hardened and high-strength steels need a bakeout after plating.
  verdict: Hard chrome is a long-used wear coating with well-documented hardness and thickness data. The bath is the main concern, and the file does not cover the deposit's own density or corrosion figures.